Friday, August 17, 2007

Could Ares rockets deflect dangerous asteroids?

Last week, NASA made headlines after publishing a report about using nuclear missiles to deflect asteroids. But the real import of the study – which was actually presented at a conference in March to little fanfare – may be in sketching out how planetary defence could be integrated into NASA's human spaceflight programme.

The agency is already thinking about sending astronauts to an asteroid. Now, a new report details three non-crewed missions to deflect asteroids, all of which rely on the Ares family of launch vehicles that NASA is developing. The Ares I (pictured) is set to deliver astronauts to the International Space Station by the middle of the next decade, while the larger Ares V would carry cargo to the Moon beginning in 2020.

How would such a mission work? If a potentially dangerous asteroid is spotted, "the first step will be to launch an observer satellite on the Ares I", writes the team, which includes four engineers from NASA's Marshall Space Flight Center in Alabama, US. The observer probe would fly by or orbit the asteroid, collecting data on its structure, composition and motion to determine if the object threatened the Earth and – if so – how it could best be deflected.

If deflection proved necessary, the study considered three possible missions using the heavy-lift Ares V. Two use the rocket as an interceptor that would deliver artillery in the form of six "generic bullets" – modules weighing about 1500 kilograms each.

By far the more controversial of the two options is a nuclear weapon that would push the asteroid away with an explosion equivalent to a megatonne of TNT. Alternatively, the bullet could simply be an inert mass that would hit the object at about 10 kilometres per second, giving it a less powerful punch. In the third option, a 100-metre solar collector could be positioned near the asteroid to focus sunlight onto its surface, evaporating material to nudge it away slowly.

The best option is far from clear and would depend on the mass and structure of the space rock as well as the amount of time remaining before impact.

But former astronaut Rusty Schweickart says the most likely threats wouldn't require nukes or such a massive interceptor. He and others argue that a better approach would be to use a gravity tug, a spacecraft that would park near the asteroid and gravitationally nudge it off its deadly course.

A gravity tractor capable of deflecting the 270-metre Apophis asteroid (which has a 1 in 45,000 chance of hitting Earth in 2036) could be launched into space on an existing Delta rocket. And small, existing launchers could also be used to deliver a series of impacts to deflect more dangerous objects, he told New Scientist.

NASA says this is only a 'paper' study, not something it is definitely planning. What do you think – do we need the 'firepower' of heavy-lift rockets to deflect asteroids, or is this just another ploy to justify the huge expense of the new family of rockets? Are the nukes the right approach?